Magnesium and zinc stable isotopes as a new tool to understand Mg and Zn sources in stream food webs

Non‐traditional stable isotopes of metals were recently shown as new dietary tracers in terrestrial and marine mammals. Whether these metal stable isotopes can be used to understand feeding habits in stream food webs is not known yet. In this study, we explored the potential of stable isotopes of essential Mg (δ26Mg) and Zn (δ66Zn) as a new tool in stream ecology. For this purpose, we determined δ26Mg and δ66Zn values of stream organisms and their potential metal sources in upper and lower reaches of two streams in the Lake Biwa catchment, Central Japan. Our goals were (1) to explore variations in δ26Mg and δ66Zn across organisms of different feeding habits and (2) to understand Mg and Zn sources to stream organisms. Overall, δ26Mg and δ66Zn values of organisms were neither related to each other, nor to δ13C and δ15N values, indicating different elemental sources and factors controlling isotopic fractionation depending on element and taxa. Low δ26Mg values in filter‐feeding caddisfly larvae and small gobies indicated aqueous Mg uptake. Higher δ26Mg values in leaf‐shredding crane fly and grazing mayfly larvae suggested Mg isotopic fractionation during Mg uptake from the diet. While the δ26Mg values of stonefly nymphs reflected those of caddisfly larvae as a potential prey, the highest δ26Mg values found in dobsonfly nymphs can be explained by 26Mg enrichment during maturing. δ66Zn values of caddisfly and mayfly larvae indicated Zn was a mixture of aqueous and dietary available Zn, while higher δ66Zn values in crane fly larvae pointed to Zn isotopic fractionation during Zn uptake from plant litter. δ66Zn values in stonefly and dobsonfly nymphs were often in the range of those of caddisfly larvae as their prey, while dragonfly nymphs and small goby were depleted in 66Zn relative to their dietary Zn sources. We conclude that δ26Mg is a promising indicator to assess Mg sources in stream ecology depending on taxa, while the use of δ66Zn is limited due to the complexity in Zn sources

Magnesium and zinc stable isotopes as a new tool to understand Mg and Zn sources in stream food webs

Non-traditional stable isotopes of metals were recently shown as new dietary tracers in terrestrial and marine mammals. Whether these metal stable isotopes can be used to understand feeding habits in stream food webs is not known yet. In this study, we explored the potential of stable isotopes of essential Mg (δ²⁶Mg) and Zn (δ⁶⁶Zn) as a new tool in stream ecology. For this purpose, we determined δ²⁶Mg and δ⁶⁶Zn values of stream organisms and their potential metal sources in upper and lower reaches of two streams in the Lake Biwa catchment, Central Japan. Our goals were (1) to explore variations in δ²⁶Mg and δ⁶⁶Zn across organisms of different feeding habits and (2) to understand Mg and Zn sources to stream organisms. Overall, δ²⁶Mg and δ⁶⁶Zn values of organisms were neither related to each other, nor to δ¹³C and δ¹⁵N values, indicating different elemental sources and factors controlling isotopic fractionation depending on element and taxa. Low δ²⁶Mg values in filter-feeding caddisfly larvae and small gobies indicated aqueous Mg uptake. Higher δ²⁶Mg values in leaf-shredding crane fly and grazing mayfly larvae suggested Mg isotopic fractionation during Mg uptake from the diet. While the δ²⁶Mg values of stonefly nymphs reflected those of caddisfly larvae as a potential prey, the highest δ²⁶Mg values found in dobsonfly nymphs can be explained by ²⁶Mg enrichment during maturing. δ⁶⁶Zn values of caddisfly and mayfly larvae indicated Zn was a mixture of aqueous and dietary available Zn, while higher δ⁶⁶Zn values in crane fly larvae pointed to Zn isotopic fractionation during Zn uptake from plant litter. δ⁶⁶Zn values in stonefly and dobsonfly nymphs were often in the range of those of caddisfly larvae as their prey, while dragonfly nymphs and small goby were depleted in ⁶⁶Zn relative to their dietary Zn sources. We conclude that δ²⁶Mg is a promising indicator to assess Mg sources in stream ecology depending on taxa, while the use of δ⁶⁶Zn is limited due to the complexity in Zn sources

Calcium and strontium stable isotopes reveal similar behaviors of essential Ca and nonessential Sr in stream food webs

Recent studies showed the potential of stable isotopes of the macronutrient calcium (δ⁴⁴/⁴⁰Ca) and nonessential strontium (δ⁸⁸/⁸⁶Sr) as new trophic level indicators in terrestrial vertebrates and marine teleost fishes. In this study, we tested whether similar Ca and Sr isotopic fractionation trends existed in macroinvertebrate-dominated stream food webs compared to vertebrates despite their physiological differences. We have determined the δ⁴⁴/⁴⁰Ca and δ⁸⁸/⁸⁶Sr values as well as the ⁸⁷Sr/⁸⁶Sr ratios of stream macroinvertebrates and small gobies and their potential metal sources (stream water, periphyton, and terrestrial plant litter) in upper and lower reaches of two streams in the Lake Biwa catchment, central Japan. The ⁸⁷Sr/⁸⁶Sr ratios revealed that stonefly nymphs, crustacea, and gobies mostly relied on aquatic Sr sources. Higher ⁸⁷Sr/⁸⁶Sr ratios of some crane fly and caddisfly larvae, mayfly, dobsonfly, and dragonfly nymphs indicated greater terrestrial contributions via plant litter. Positive correlations between the δ⁴⁴/⁴⁰Ca and δ⁸⁸/⁸⁶Sr values implied that similar Ca and Sr sources existed, and that Ca and Sr stable isotopes underwent similar fractionation trends although Sr was not essential. The δ⁴⁴/⁴⁰Ca and partly the δ⁸⁸/⁸⁶Sr values were positively correlated with Sr/Ca ratios and negatively with δ¹⁵N values indicating trophic effects on Ca and Sr stable isotopes. The enrichment of ⁴⁴Ca and ⁸⁸Sr in large filter-feeding caddisfly larvae was a notable exception from these trophic trends. Our data confirm that the trophic ⁴⁴Ca and ⁸⁸Sr depletion observed for marine teleost fishes and terrestrial vertebrates also applied to macroinvertebrate-dominated stream food webs despite their different physiologies indicating that shared mechanisms of Ca and Sr isotopic fractionation may exist at the cellular or molecular level between these taxa

Effects of inorganic mercury and methylmercury on osteoclasts and osteoblasts in the scales of the marine teleost as a model system of bone

To evaluate the effects of inorganic mercury (InHg) and methylmercury (MeHg) on bone metabolism in a marine teleost, the activity of tartrate-resistant acid phosphatase (TRAP) and alkaline phosphatase (ALP) as indicators of such activity in osteoclasts and osteoblasts, respectively, were examined in scales of nibbler fish (Girella punctata). We found several lines of scales with nearly the same TRAP and ALP activity levels. Using these scales, we evaluated the influence of InHg and MeHg. TRAP activity in the scales treated with InHg (10-5 and 10-4 M) and MeHg (10-6 to 10-4 M) during 6 hrs of incubation decreased significantly. In contrast, ALP activity decreased after exposure to InHg (10-5 and 10-4 M) and MeHg (10-6 to 10-4 M) for 18 and 36 hrs, although its activity did not change after 6 hrs of incubation. As in enzyme activity 6 hrs after incubation, mRNA expression of TRAP (osteoclastic marker) decreased significantly with InHg and MeHg treatment, while that of collagen (osteoblastic marker) did not change significantly. At 6 hrs after incubation, the mRNA expression of metallothionein, which is a metal-binding protein in osteoblasts, was significantly increased following treatment with InHg or MeHg, suggesting that it may be involved in the protection of osteoblasts against mercury exposure up to 6 hrs after incubation. To our knowledge, this is the first report of the effects of mercury on osteoclasts and osteoblasts using marine teleost scale as a model system of bone. © 2014 Zoological Society of Japan

森は海の恋人か？土地利用変化と河川流量及び海域変化の統合研究スキームの開発

金沢大学環日本海域環境研究センター本研究の目的は、明治以降の大規模な土地利用改変に対する河川及び汽水湖生態系の反応を、汽水湖の堆積物コア解析や古文書、統計資料、数理モデル等を駆使して復元することにより、水系全体の動態予測と再生指針の構築に資することである。厚岸湖集水域の土地利用変化を解析し、農地が第二次大戦後に大幅に増加したことを明らかにした。また、河川流況モデルのパラメータ検討の一環として、流入河川の結氷状況と、海霧による蒸発散の低下範囲を推定した。厚岸湖の堆積物コアで年代測定と同時に有殻性プランクトン相の復元を試み、現在貝毒被害を生じている有毒種がかなり以前から定着していることを明らかにした。The object of this project was reconstructing the past interaction between large-scale land-use change and river discharge or coastal marine ecosystem through combination of analyzing sediment core at lagoon, old references, governmental statistics or numerical models. It may helpful to understanding the dynamics of aquatic systems after areal reclamation or constructing the direction for reconstruction after large-scale development.We found that farmland drastically increased after the World War Two by analyzing the long-term change of land-use in Akkeshi lake watershed (Hokkaido, Japan) where is the study area. We also examined the freezing area among inlets, covering area by sea-fog which dropping evaporation or transpiration. Reconstruction of plankton flora which having shells by DNA extraction, which running with age estimation, showed several harmful species that causing shellfish poisoning in the present has been inhabiting since a long time ago through sediment core analysis.研究課題/領域番号:26550088, 研究期間(年度):2014-04-01 - 2017-03-3